This application claims the benefit of Korean Application Nos. 2001-13300, filed Mar. 15, 2001 and 2002-5068, filed Jan. 29, 2002, in the Korean Industrial Property Office, the disclosures of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to compressors, and more particularly, to a compressor having a driving mechanism for linearly reciprocating a piston and a method for controlling the same.
2. Description of the Prior Art
In general, compressors are used to suck, compress and discharge a gas such as a vaporized refrigerant in apparatuses utilizing a refrigeration cycle, such as refrigerators and air conditioners. The compressors can be classified into linear compressors, reciprocating compressors, and rotary compressors. The linear compressors equipped with linear motors as their driving mechanisms have relatively high energy efficiencies due to a low energy loss in their driving mechanisms.
FIG. 1 shows the interior construction of a conventional linear compressor. The conventional linear compressor comprises a driving mechanism 3 which generates power in an airtight container 1 and a compressing mechanism 2 which sucks and compresses a refrigerant using the power transmitted from the driving mechanism 3.
The compressing mechanism 2 includes a cylinder block 2b provided with a compression chamber 2a therein, and a cylinder head 2c coupled to the upper portion of the cylinder block 2b so as to guide the refrigerant being sucked and discharged. Additionally, a piston 2d which linearly reciprocates in response to an operation of the driving mechanism 3 is arranged in the compression chamber 2a. 
The driving mechanism 3, which is a kind of a linear motor, includes a tubular back iron 3d arranged outside of the cylinder block 2b, a core 3b spaced apart from the tubular back iron 3d having a wound coil 3a which forms a magnetic field in response to an applied power, and a magnet 3c arranged between the core 3b and the tubular back iron 3d which moves up and down.
The core 3b is composed of a plurality of layered electrical steel sheets, whose upper and lower portions are supported by a first frame 2e which outwardly extends from the upper portion of the cylinder block 2b and a second frame 2f fixed to the first frame 2e by bolts 4, respectively. The magnet 3c linearly reciprocates through interaction with the magnetic field formed by the core 3b, and is connected to the piston 2d through a connection rod 5. The piston 2d reciprocates in the compression chamber 2a by the reciprocating movement of the magnet 3c. 
The compressing mechanism 2 and the driving mechanism 3 are supported by coil springs 6 and a resonance spring 7 that elastically support the cylinder block 2b in the lower portion of the interior of the airtight container 1. That is, the coil springs 6 which elastically support the cylinder block 2b in the lower portion of the interior of the airtight container 1 are arranged under spacers 8 placed under the second frame 2f so as to position the piston 2d. 
The resonance spring 7 is a kind of a leaf spring, whose peripheral portions are attached to the spacers 8 and whose center portion is connected to the piston 2d. The resonance spring 7 enhances the power to reciprocate the piston 2d and oscillates with the piston 2d in upward and downward directions (directions indicated by the arrows of FIG. 1).
However, the driving mechanism 3 which linearly reciprocates the piston 2d comprises a linear motor that requires a considerable-sized core and magnet to obtain a desired output. Furthermore, the structure of the linear motor is complicated.
Accordingly, the overall size of the conventional linear compressor is large and hinders the compressor from being mounted within apparatuses such as refrigerators. Additionally, the manufacturing process of a driving mechanism for a conventional linear compressor is complicated, making the performance of the compressor dependent on the complicated manufacturing process of the driving mechanism.
In addition, the piston 2d of the conventional linear compressor is operated to desired displacements by phase-controlling the driving mechanism 3 comprises a linear motor. For such an operation, the linear motor requires additional displacement sensors (not shown) to sense the displacements of the magnet 3c and the piston 2d. As a result, the linear compressor is problematic in that other portions of the compressor are restricted to a narrow installation space due to the displacement sensors being mounted in the airtight container 1. Moreover, the displacement sensors may undergo an integer variation due to temperature, and it is difficult to control the integer variation.
Accordingly, it is an object of the present invention to provide a compressor with an improved driving mechanism which linearly operates a piston, and allows the compressor to be miniaturized and easily manufactured.
It is another object of the present invention to provide a method of controlling a compressor provided with an improved driving mechanism for linearly operating a piston, which is capable of allowing the driving mechanism to be easily controlled.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
To achieve the above and other objects of the present invention there is provided a compressor comprising a cylinder block having a compression chamber, a piston arranged in the compression chamber which reciprocates up and down, and a driving mechanism which drives the piston and comprises an elastic member whose peripheral portions are fixed to the cylinder block so as to allow the elastic member to oscillate up and down and whose center portion is attached to the piston, and one or more piezoelectric actuators arranged on the elastic member which repeatedly deform in response to a power and apply an exciting power to the elastic member.
To achieve the above and other objects of the present invention there is provided a method of controlling a compressor comprising a cylinder block having a compression chamber, a piston positioned in the compression chamber which reciprocates up and down through the compression chamber, an elastic member whose peripheral portions are fixed to the cylinder block so as to allow the elastic member to oscillate up and down and whose center portion is attached to the piston, and one or more piezoelectric actuators arranged on the elastic member which repeatedly deform in response to a power and apply an exciting power to the elastic member, the method comprising sensing a displacement of the elastic member through deformations of the piezoelectric actuators and controlling the displacement of the elastic member by adjusting an amount and/or frequency of an electric voltage applied to the piezoelectric actuators.